1. Field of the invention:
The invention relates to a valve device for controlling the delivery of pressurized liquid to two separate hydrostatic motors from a common source of pressurized liquid which is variable in respect of pressure.
2. Prior Art:
In certain kinds of working machines, for example, two or more simultaneously operating hydrostatic working motors are supplied from a common pump, the load on one of the motors varying in dependence on a working parameter, such as the speed, of another working motor. A concrete sawing machine of the type used for cutting openings in concrete walls and the like may be taken as an example of such a working machine.
A known embodiment of such sawing machines has a main drive motor in the form of a hydrostatic rotary motor mounted on a movable carriage and driving a diamond saw blade. Moreover, the sawing machine has a feed motor which is also mounted on the carriage and takes the form of a rotary motor, preferably reversible, serving to displace the carriage in either direction on guides secured to the wall or the like to be cut. An additional feed motor may also be provided which serves to displace the saw blade transversely of the plane in which the carriage is moved.
As is readily appreciated, the rate of feed, that is, the speed of the carriage, has to be matched with the nature of the material to be cut, the properties of the saw blade, and so on. In the known sawing machines, however, this requirement cannot be met reliably with reasonably simple means. This is so at least in the frequent instances where the sawing properties vary from one sawing operation to the next or in the course of one and the same sawing operation. For example, when cutting lightweight concrete, the rate of feed may of course be much higher than when cutting ordinary concrete. In the latter instance, the sawing properties may vary in the course of the sawing operation, e.g. at the locations where steel reinforcement bars have to be cut. The problem is aggravated because the force required to displace the carriage (disregarding the cutting force) may vary for various reasons, e.g. because the guides are misaligned or because the power transmission becomes dirty with concrete dust and jams.